Subsurface tubing well safety valves are used in wells for shutting off the flow of well fluid through the well tubing in which the valve is biased to a closed position and is opened by a piston in response to hydraulic control fluid applied from the well surface. However, the means biasing the valve to a closed position must overcome the hydrostatic head in the hydraulic control line to the piston. My prior U.S. Pat. No. 4,161,219 discloses the use of one or more pistons having a small cross-sectional area which reduces the hydrostatic force of the hydraulic control fluid whereby the safety valve may be used at greater depths in the well. Therefore, by reducing the cross-sectional area of the pistons, the hydrostatic forces may be reduced. However, reducing the cross-sectional area of the control pistons increases the compression loading in the piston rods and can cause the piston rods to bend or buckle thereby causing the safety valve to fail to operate.
The present invention is directed to an improved piston actuated subsurface tubing safety valve which utilizes a small area piston for reducing the hydrostatic forces but provides a structure in which the piston rod operates in tension instead of compression thereby allowing the control pistons to carry greater overall loads.
The present invention is directed to a well tubing safety valve for controlling the fluid flow through a well tubing and includes a tubular housing having a bore therein and a valve closure member moving between open and closed positions for closing the fluid flow through the bore. A longitudinal tubular member telescopically moves in the housing coaxially with the bore for controlling the movement of the valve closure member. Biasing means biases the tubular member in a first direction for causing the valve closure member to move to the closed position. The present invention is directed to the improvement in means for moving the tubular member in a second direction for opening the valve closure member and includes at least one piston telescopically movable in the housing which is in communication with hydraulic fluid extending through the well surface for actutating the member in the second direction to open the valve member. The piston has a small cross-sectional area for reducing the hydrostatic force of the hydraulic fluid acting on the piston. The piston includes a piston rod extending upwardly from the piston for connection to the tubular member whereby the piston rod and piston is acted on in tension by the hydraulic fluid to move the tubular member to the open position thereby allowing the piston rod and piston to carry greater loads than if they were operating in compression.
Still a further object of the present invention is wherein the connection between the piston rods and the tubular member includes at least one telescopically movable elongate member having a greater cross-sectional area than the piston rod and is connected between the piston rod and the tubular member. The elongate member is pressure balanced relative to both the hydraulic fluid and the tubing pressure in the bore whereby the elongate member can be of a sufficient area to withstand compression loads but is not affected by the hydraulic control fluid or the tubing pressure.
Yet a still further object of the present invention is wherein the elongate member includes a piston at each end and a hole extending through the elongate member for balancing the hydraulic control fluid on the elongate member and the elongate member is exposed to the tubing pressure between the elongate member pistons thereby balancing the tubing pressure on the elongate member.
Still a further object of the present invention is the provision of a stop means on the piston on the side remote from the upwardly extending piston rod for preventing compression loading on the piston and piston rod in the event the tubing pressure is greater than the pressure of the hydraulic control fluid.
Yet a still further object of the present invention is the provision of a lost motion connection between the piston rod and the elongate member for preventing compression loading on the piston rod during the closing of the valve, but still allowing the piston and piston rod to assist in closing the valve in the event that the tubular member becomes stuck.
Other and further objects, features and advantages will be apparent from the following description of a presently preferred embodiment of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.